Electric discharge device



v Aug. 4, 1942. H. T. MASER ELECTRIC DISCHARGE DEVICE Filed Oct. 50, 1941 Ihventor Harold T. Maser,

His Attorn ey.

Patented Aug. 4, 1942 ELECTRIC DISCHARGE DEVICE- Harold T. Maser, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application October 30, 1941, Serial No. 417,120

6 Claims.

This invention relates to electric discharge devices of the type in which a discharge takes place in the presence of a condensible ionizing medium, such as mercury, and is an improvement on the invention of United States Patent 2,091,915, granted August 31, 1937, in the name of Thomas A. Elder.

As is pointed out in the aforesaid patent the ability of discharge devices which contain mercury or asimilar condensible ionizing medium to withstand inverse voltages is largely dependent upon the vapor pressure of the medium. For this reason, it is important in metal enclosed devices, the walls of which tend to run at high temperature, that some means be provided for continuously condensing a portion of the vapor content so as to regulate by this means the pressure maintained within the discharge enclosure. The Elder patent discloses as a particular means for accomplishing this function a metal tubulation projecting from the bottom of the discharge vessel and having heat-dissipating means mounted on its lower end so that the tubulation acts as a constant temperature condenser.

My present invention is primarily concerned with providing an arrangement of the general character of that described in the Elder patent wherein the condensing structure may be additionally employed as an electrical terminal for one of the discharge electrodes, thereby permitting a simplified and less costly construction of the device as a whole. This is accomplished in one embodiment of the invention by separating the part intended as a condenser from the main body of the envelope by insulating means and providing an electrical connection between the thus insulated part and the selected electrode. This arrangement is found advantageous, for example, in providing a connection to the heating element of an indirectly heated cathode forming one electrode of a mercury vapor discharge tube.

The features of the invention which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, together With further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. l is a longitudinal section of a discharge device suitably embodying the invention; Fig. 2 is an enlarged section of the cathode structure of Fig. 1; Fig. 3 is a fragmentary section showing on a magnified scale the condensing arrange 55 ment of Fig. 1; and Fig. 4 is a section taken on line 44 of Fig. 3.

Referring particularly to Fig. 1 there is shown a metal envelope comprising a section of steel tubing l which is closed at its upper and lower ends by flanged headers indicated at II and I2 respectively. Within the envelope and at the upper end thereof there is provided an anode M which may suitably comprise a graphite disk. This is mounted on a heavy conductive rod [5 and is insulatingly supported from the header I I through a glass sleeve ll. The sleeve I1 is hermetically joined to the header by means of a flanged metal cylinder l8 which is sealed to the sleeve and welded to the header, and it is closed at its upper extremity by means of a metal cap 20. A flexible conductor 22 is secured to the cap by being soldered into a metal ferrule 23 which is affixed to the cap.

At the lower end of the envelope there is provided a cathode 25 having its active parts enclosed within a metal heat shield 26 (Fig. 2). The structure of the cathode includes a pair of metal support rods 21 on which are mounted two spaced metal rings 28. The rings are provided externally with an array of radially projecting studs 29, and these serve as a framework for a zigzag metal ribbon 30, the surfaces of the ribbon being preferably coated with an electronically active material such as an alkaline earth oxide.

In use the ribbon 30 is maintained in emissive condition by heat radiated from a filamentary resistance heater 3| which is arranged centrally within the cathode and which is supported at its upper extremity by connection to a metal strip 32 affixed to the support rods 27. These rods, which form in effect one terminal of the resistance heater, are grounded directly to the envelope header l2 by being welded to metal brackets 33. A second terminal for the heater is provided by extending the lower end of the heater filament through the bottom of the cathode heat shield as indicated at 34. The various conductive parts are electrically separated from one another and from the heat shield by means of appropriately positioned insulators 35 and 36. In the operation of the device the initiation of a discharge between the cathode 25 and the anode I4 is controlled by means of a grid in the form of a conductive cylinder 3'! which is disposed between them. This grid is rigidly mounted with respect to the main body of the envelope by means of a heavy conductor 38 which is insulatingly supported from the envelope through a glass sleeve 39. In addition to the sleeve 39 the supporting structure includes a metal cap 40 and a metal cylinder 4|, these elements being hermetically joined to the respective extremities of the sleeve. Apertured metal baflies 44 arranged within the discharge envelope on opposite sides of the grid 31 serve to shield the grid and to make its action more consistent and reliable.

The operation of the device in its intended manner requires the presence within the discharge space of a readily ionizable medium, and in the present instance the substance employed for this use consists of a quantity of mercury. As has been previously stated herein, it is essential that the pressure of the mercury be kept relatively low in order to avoid the possibility of arc-back. This is a condition which is difficult to fulfill in a metal-enclosed tube structure for the reason that the various metal surfaces tend to run at a uniformly high temperature and thus afford no opportunity for condensation of the mercury. This difiiculty is overcome in the construction of Fig. 1, however, by providing in connection with the discharge envelope an external container in which the excess mercury may be condensed and held at relatively constant temperature. The container is in the form of a metal (e. g. steel) tubulation 46 which depends from the closure member I2 and which is closed at its lower end by a pinch-welded tube 41 used during fabrication for finally evacuating and sealing ofi the discharge envelope. In order that the tubulation 46 may be maintained at a relatively low temperature there is provided in effective heat-exchanging relation with it a heatdissipating structure in the form of a vaned radiator 48, this latter part suitably consisting of a highly conductive metal such as copper. The radiator is joined to the lateral wall of the tubulation 46 by the interposition of a layer of solder 50 and serves to maintain the tubulation at a temperature low enough so that the mercury is condensed and retained in it as indicated at 52 Under these conditions the mercury vapor pressure within the main body of the discharge en- I velope is essentially determined by the temperature of the liquid mercury at 52.

In order to minimize h'eat fiow from the main body of the metal envelope III to the tubulation 46 and thence to the mercury 52 the tubulation is thermally insulated from the envelope structure by means of a glass cylinder 54. This cylinder is joined to the tubulation through a, connecting metal sleeve 55 and is supported from the closure member l2 by means of a similar sleeve 56. It will be understood, of course, that the joints of the various parts referred to are made vacuumtight by welding the parts together in an appropriate manner.

Insulation of the tubulation 46 from the discharge envelope in the manner specified makes it possible for the tubulation to serve a secondary function; namely, that of a current supply terminal for the resistance heater 3|. To this end, there is provided an electrical connection between the tubulation and one terminal of the heater, this connection being shown in the form of a wire 58 which terminates at its lower end in a circular loop portion 58' welded or otherwise secured to the upper end of the tubulation. The wire 58 extends into engagement with the terminal 34 of the cathode heater and is conductively connected to it as indicated at 59. By virtue of this arrangement the cathode heater may be energized by impressing potential between the structure of the radiator 48 and the main body of the envelope. For use in this connection, there is provided in conjunction with the radiator a terminal lug 60 which connects with a first flexible conductor 6|, and a second flexible conductor 62 is attached to a heavy stud 63 which depends from the lower end of the envelope cylinder I0. The conductor 62 bears a number of insulating beads 64 which serve to guard it from casual contact with other metallic parts.

It will be seen that the arrangement described leads to a very simple construction in which the single glass insulator 54 serves the joint function of thermally insulating the condensing tubulation 46 from the main body of the envelope and of making the tubulation an electrically independent element to which a current supply connection for the cathode structure may be made. In addition, as has been previously specified, the tubulation provides a means of connecting the discharge enclosure to a vacuum pump during the process of fabricating the device. As a result of these various functions in a single structural part the overall cost of the apparatus is considerably diminished.

While the invention has been described by reference to a particular embodiment of it, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A discharge device comprising an envelope containing a, quantity of a condensible ionizing medium, electrode structure within the envelope, a metal container outside the envelope and connected with the space enclosed by it, whereby the container is adapted to serve as a condenser for said ionizing medium, means insulatingly separating said conductor from the main body of the envelope and an electrical connection between said container and said electrode structure whereby the container further serves as a current supply terminal for the electrode structure.

2. A discharge device comprising an envelope constituted principally of metal and containing a quantity of a condensible ionizing medium, electrode structure including a cathode within the envelope, a metal container supported by and outside of the envelope and connected with the space enclosed by it so that the container is adapted to serve as a condenser for the said ionizing medium, means insulatingly separating the said container from the metallic parts of the envelope, whereby the temperature of the container is relatively independent of the temperature of the envelope, and an electrical connection between the said container and the cathode, whereby the container is further adapted to serve as a current supply terminal for the cathode.

3. A discharge device comprising an envelope having a metallic closure member at the lower extremity thereof, electrode structure including a cathode within the envelope, a quantity of a condensible ionizing medium also within the envelope, a hollow metal tubulation depending from said closure member, said tubulation being in gaseous communication with the interior of said envelope so that it is adapted to receive said ionizing medium when in condensed state, means insulatingly separating the tubulation from the said closure member, whereby the temperature of the tubulation is substantially independent of that of the closure member, and an electrical connection between said tubulation and said cathode, whereby the tubulation serves as a current supply terminal for the cathode.

4. A discharge device comprising a metal envelope containing a quantity of a condensible ionizing medium, electrode structure within the envelope, a metal tubulation projecting outwardly from a metal wall portion of said envelope and in gaseous communication with the interior of the envelope, said tubulation being insulated from the main body of the envelope, a heat-dissipating structure in thermal contact with the tubu1a tion whereby the tubulation is adapted to serve as a condenser for said ionizing medium, and an electrical connection between said tubulation and said cathode whereby the tubulation is further adapted to serve as a current supply terminal for the said electrode structures.

5. A discharge device comprising an envelope in the form of an elongated metal cylinder having a metal closure member at its lower end, electrode structure including a cathode within the said envelope, resistance heating means forming a part of the said cathode and having one terminal thereof connected to the said envelope, a tubulation depending from said metal closure member and in gaseous communication with the interior of the envelope, said tubulation consisting of metal and there being a glass sleeve insulatingly separating the tubulation from the closure member, whereby the tubulation is adapted to serve as a condenser for said ionizing medium, and an electrical connection between said tubulation and the other terminal of said resistance heater, whereby said heater may be energized by application of potential between said tubulation and said envelope.

6. A discharge device comprising an elongated envelope consisting principally of metal, a quantity of condensible ionizing medium within the envelope, electrode structure including a cathode also within the envelope, a resistance heater forming a part of the cathode and having one terminal connected directly to the envelope, 2. tubulation depending from the lower end of the envelope and communicating with the interior of the envelope, a glass sleeve insulating said tubulation from the main body of the envelope, 2. metal radiator in eiTective heat-exchanging engagement with the tubulation whereby the tubulation is adapted to serve as a condenser for said ionizing medium, and an electrical connection between said tubulation and the other terminal of said resistance heater.

HAROLD T. MASER. 

